Mazda 4-Rotor Rotary Engine for the Le Mans 24 …

1 920309. Mazda 4-Rotor Rotary Engine for the Le Mans 24-Hour Endurance Race Ritsuharu Shimizu, Tomoo Tadokoro, Toru Nakanishi, and Junichi Funamoto Mazda Motor Corp 920309. Mazda 4-Rotor Rotary Engine for the Le Mans 24-Hour Endurance Race Ritsuharu Shimizu, Tomoo Tadokoro, Toru Nakanishi, and Junichi Funamoto Mazda Motor Corp. powered by an R26B Engine , scored the overall victory ABSTRACT with a sustained full-power run. This paper reviews the basic construction of this Engine and the technologies The "R26B" 4-Rotor Rotary Engine is a powerplant that developed to improve its power output, fuel consump- brought a Mazda racing car to victory in the 1991 Le tion, and reliability. Mans 24-hour endurance race. This Engine was devel- oped to achieve high levels of power output, fuel effi- ciency, and reliability, as required of endurance racing engines. This paper describes the basic structure of the Engine , including a 3-piece eccentric shaft that repre- sents a major technological achievement incorporated in the Engine , as well as other technological innovations employed for the enhancement of the Engine 's power output and reliability, and for reducing its fuel consump- tion.

2 These innovations include a telescopic intake mani- fold system, peripheral port injection, 3-plug ignition system, 2-piece ceramic apex seal, and a cermet coating on the rubbed surfaces of the housings. INTRODUCTION. It was in 1967 when Mazda first launched a 2-rotor en- Fig. 1 Mazda 787B. gine car. Since 1968, we have been a serious participant in motor sport events to achieve engineering gains that OBJECTIVES OF DEVELOPMENT AND. could ensure the Rotary Engine 's durability and reliabil- TECHNOLOGIES USED. ity. The Rotary Engine , starting its life as a 2-rotor unit, has ever increasingly evolved at Mazda into an Engine of To ensure that the R26B Engine achieved simultaneous higher level of performance, with 3-rotor and 4-Rotor improvement of output, fuel consumption, and reliabil- units added in recent years. ity, while meeting Category 2 regulations, the following The 1991 Le Mans 24-hour endurance race, an event were set as primary development objectives: in the Sportscar World Championship series was held (1) Enhancing Output Performance and Throttle Re- with two category entrants competing together.

3 Cate- sponse gory 1 covered naturally-aspirated cars up to dis- The main objective here was to realize a substan- placement and Category 2 represented cars which were tial increase in power output, while providing a free to have any type, configuration, and layout of en- wide torque range and a quick throttle response, gine, while constrained only by a maximum of 2550 li- thus easing driver control of the vehicle. tres of gasoline available for consumption during the race. The 4-Rotor Engine , "R2613", was developed to meet the Category 2 regulations. A Mazda 787B (Fig. 1), (2) Improving Fuel Consumption The objectives were to reduce fuel consumption and to realize a fuel control system suitable for cir- cuit driving, thus improving total fuel consumption. (3) Securing Durability and Reliability The third target was to realize a high level of reli- ability :hat would allow the car to withstand, with some margin, a continuous 24-hour 5000-km run at full power; in other words, enduring the rigors of the Le Mans race.

4 The technologies developed to meet the above objec- tives are diagrammatically shown in Fig. 2. Engine SPECIFICATIONS. Table 1 lists the specifications of the R26B Engine . It is a naturally-aspirated 4-Rotor unit designed to balance power output and fuel efficiency, while having other attributes, required of a racing Engine such as maximum ease of installation and servicing. Fig. 2 Objectives of development and principal technolo- gies (1) OUTLINE OF Engine . Fig. 3 is a photo of the R26B, and Fig. 4 a sectional view. The 4-Rotor Engine is common in trochoid configu- Table 1 Main data of R26B Engine ration and unit chamber volume with Mazda 's produc- tion Rotary engines on which it is based. The rotor, de- signed for a compression ratio of 10:1, is precision-cast, using the lost wax process to reduce the mass of the rotating system. The rotor and side housings have cermet-coated in- ternal surfaces.

5 The apex seal, made of ceramics, is a 2-piece type designed for enhanced reliability and gas sealing. Fig. 3 Photo of the R26B. Fig. 4 Sectional view of R26B. For induction, the Engine employs peripheral ports for good volumetric efficiency, with a sliding throttle valve used for low restriction in wide-open throttle (WOT) op- eration. Another feature is the telescopic intake mani- fold system (TIMS), the first of its kind ever used on a racing Engine . (2) Engine CONTROL SYSTEM. The Engine control system used on the R26B is illus- trated in Fig. 5. The main control parameters are fuel injection volume, injection timing, ignition timing, tele- scopic intake pipe length, number of fuel pumps, power generation, failsafe system, diagnostics, fuel consump- tion monitoring, and data transfer. To measure intake air amount, the Engine employs the a-N method which uses throttle opening and Engine speed as parameters.

6 The fuel control system, in addition to controlling fuel injection, volume and timing, handles air/fuel ratio feedback. This ensures the fuel delivery to be free from the effects of external turbulence throughout the driving range, thus allowing the Engine to be operated at the Fig. 5 Engine control system of R26B. targeted air/fuel ratios. Engine PERFORMANCE. The R26B Engine 's performance curves are shown in Fig. 6. Its maximum output is 515 kW at 9000 rpm with a peak torque of 608 Nm at 6500 rpm. By having the air-fuel ratio, fuel injection timing, and ignition timing optimized for efficiency, a minimum fuel consumption of 286 g/kWh at 6000 rpm was obtained. Fig. 7 Eccentric shaft For rotational balancing, a counterweight is used at the front and rear of the eccentric shaft. Fig. 8 shows ex- amples of rotor phase angles and the required counter- weights.

7 Taking the rotating counterweights and torque variations into consideration, ignition spacing of 90 de- grees was provided for an ignition sequence of 1-3-2-4. Fig. 6 Engine performance curve of R26B Fig. 8 Balancing of 4 rotors (Relation between rotor phase angle and counterweight). TECHNOLOGIES DEVELOPED To compensate for the reduced stiffness that the addi- tional length of the 4-Rotor Engine might cause, and to (1) 4-Rotor Engine increase the total stiffness of the Engine , the tension bolts for the No. 1 and rotor housings and those The most important task faced in designing a Rotary en- for No. 3 and No. 4 were anchored in their respective gine with three or more rotors was how best to assem- center housings. This construction technique also helped ble the rotors in the rotor housings. Although a multiro- facilitate the process of Engine dismantling and reas- tor Engine could be built by employing one of several sembly for servicing.

8 To further increase Engine stiffness methods, including the use of a built-up eccentric shaft while still holding down added weight, an aluminum oil via Curvic coupling, splining, etc., and a split stationary pan of honeycomb design was adopted and was in- gear or split bearing, a taper coupling was developer stalled atop the Engine . Also, a stiffener of aluminum that proved superior in reliability and integrity. This type honeycomb cores sandwiched between carbon plates of eccentric shaft has been in use since 1986, starting was incorporated. with a 3-rotor racing Engine .(1) As shown in Fig. 7, the R26B's eccentric shaft comprises three pieces: a main Engine coolant enters the Engine through the center shaft with and rotor journals, and hollow end housing and is diverted into the two rotor housings, one shafts at the front and at the rear, having rotor journals fore and one aft, before returning to the center housing.

9 For the and rotors , respectively. The hollow Lubricating oil also enters the center housing and flows front and rear shafts are taper-coupled to the main into the front and rear pairs of rotor housings so that an shaft. equal amount of lubricant circulates through the hous- ings, thus ensuring uniform temperature distribution. (2) TELESCOPIC INTAKE MANIFOLD SYSTEM controls the DC motors to make the funnels move to the (TIMS) position which will provide the induction pipe the length predetermined for a given Engine speed. It is a well known fact that the dynamic effect of intake airflow can be used to increase volumetric efficiency. The system adopted by Mazda employs telescopically- variable intake pipes, where the length of the pipes var- ies steplessly to match Engine speed, thus providing a dynamic effect over a wider Engine speed range. The telescopic intake manifold system, schematically shown in Fig.

10 9, consists of cylindrical pipes inside which air funnels can slide. The length of the four intake pipes is controlled by varying the position of the air funnels. The sliding air funnels are as thin-walled as possible, and there are no protrusions in the air passages so as to minimize changes in airflow. The sliding air funnels for No. 1 and No. 2 rotors are interconnected via a linear ball bearing, as are those for rotors No. 3 and No. 4. The linear ball bearing is ar- ranged such that it slides along a guide projecting from the stationary pipe side, thus positioning the air funnels in their appropriate locations. Fig. 11 Induction pipe length vs Engine speed Fig. 11 plots induction pipe length as a function of Engine speed. Note that the length varies from its most extended position to the shortest over a range of 2500. rpm. The system completes the sliding operation in s, which is sufficiently quick to follow, at minimum, full- power acceleration in second gear.